The self inductance is a kind of electromagnetic induction. Self inductance is defined as the induction of a voltage in a current carrying wire when the current in the wire itself is changing, the magnetic field created by a changing current in the circuit itself induces a voltage in the same circuit. Therefore, the voltage is self induced.

The common inductor is a coil of wire. Figure 4 shows the a coil carrying alternating current creating a magnetic field in and around the coil that is increasing and decreasing as the current changes. This causes a voltage to be induced in the coil when the current is changing.

Figure 4

The induced voltage depends on the number of turns in the coil:

V_L = N d Φ/d t …………………………… (6-6)

Where V_L = induced voltage (V)

N = number of turns in the coil

d Φ/d t = rate of change of magnetic flux (Wb/s)

It is easier to measure current than it is measure magnetic flux, and equation (6-3) can be modified to:

V_L = L d i/d t ………………………………. (6-7)

Where V_L = induced voltage (V)

L = inductance (Henry)

d i/ d t = rate of change of current (A/s)